From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from d28relay02.in.ibm.com (d28relay02.in.ibm.com [9.184.220.59]) by e28esmtp04.in.ibm.com (8.13.1/8.13.1) with ESMTP id m1L5AZPI000377 for ; Thu, 21 Feb 2008 10:40:35 +0530 Received: from d28av04.in.ibm.com (d28av04.in.ibm.com [9.184.220.66]) by d28relay02.in.ibm.com (8.13.8/8.13.8/NCO v8.7) with ESMTP id m1L5AZ1j1134654 for ; Thu, 21 Feb 2008 10:40:35 +0530 Received: from d28av04.in.ibm.com (loopback [127.0.0.1]) by d28av04.in.ibm.com (8.13.1/8.13.3) with ESMTP id m1L5AZHl020752 for ; Thu, 21 Feb 2008 05:10:35 GMT Message-ID: <47BD06C2.5030602@linux.vnet.ibm.com> Date: Thu, 21 Feb 2008 10:36:10 +0530 From: Balbir Singh Reply-To: balbir@linux.vnet.ibm.com MIME-Version: 1.0 Subject: Re: [PATCH] Document huge memory/cache overhead of memory controller in Kconfig References: <20080220122338.GA4352@basil.nowhere.org> <47BC2275.4060900@linux.vnet.ibm.com> <200802211535.38932.nickpiggin@yahoo.com.au> In-Reply-To: <200802211535.38932.nickpiggin@yahoo.com.au> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Andi Kleen , akpm@osdl.org, torvalds@osdl.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Nick Piggin wrote: > On Wednesday 20 February 2008 23:52, Balbir Singh wrote: >> Andi Kleen wrote: >>> Document huge memory/cache overhead of memory controller in Kconfig >>> >>> I was a little surprised that 2.6.25-rc* increased struct page for the >>> memory controller. At least on many x86-64 machines it will not fit into >>> a single cache line now anymore and also costs considerable amounts of >>> RAM. >> The size of struct page earlier was 56 bytes on x86_64 and with 64 bytes it >> won't fit into the cacheline anymore? Please also look at >> http://lwn.net/Articles/234974/ > > BTW. We'll probably want to increase the width of some counters > in struct page at some point for 64-bit, so then it really will > go over with the memory controller! > Hmm... > Actually, an external data structure is a pretty good idea. We > could probably do it easily with a radix tree (pfn->memory > controller). And that might be a better option for distros. > I'll put in my long list of TODOs. I started looking at it yesterday again and here are my early thoughts 1. We could create something similar to mem_map, we would need to handle 4 different ways of creating mem_map. 2. On x86 with 64 GB ram, if we decided to use vmalloc space, we would need 64 MB of vmalloc'ed memory I have not explored your latest suggestion of pfn <-> memory controller mapping yet. I'll explore it and see how that goes. -- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org